Well, you can do it in XP, partially. You can "blow away" the partition with Windows disk management. Then boot from the XP install CD, enter the repair console and use DiskPart to expand the remaining partition.
Diskpart will only work if the partition is NTFS. On a machine that was set to dual boot with OS/2, I wouldn't count on the XP partition being NTFS.
It's a whole lot quicker and easier to just get the free EaseUS Partition Master software from the link I provided and use that.